The complement-derived chemotactic factor from zymosan-activated serum will be isolated, purified, and structurally defined. Abnormalities of leukotactic function in caner-bearing rats will be studied and quantitative measurements made of the defects in these animals to mobilize inflammatory cells. Finally, an in vitro model of infection of red cells by the protozoan Babesia rodhaini will be developed and the complement requirement of this model determined.